[Shell] shell中的內部變數

1.BASH二進位制執行檔案的位置,版本
[root@oracle6 /]# echo $BASH
/bin/bash
[root@oracle6 /]# echo $BASH_VERSION
4.1.2(1)-release

2.home目錄
[root@oracle6 /]# echo $HOME
/root

3.$? : shell command的返回值
[root@oracle6 /]# ping 172.16.20.31            這個ip能ping通
--- 172.16.20.31 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1931ms
[root@oracle6 /]# echo $?
0
[root@oracle6 /]# ping 172.16.20.33            這個ip不能ping通
PING 172.16.20.33 (172.16.20.33) 56(84) bytes of data.
^C
--- 172.16.20.33 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 3583ms


[root@oracle6 /]# echo $?
1

4.$$ : 獲取當前shell的pid
[root@oracle6 /]# echo $$
27947

5.$! : 獲取當前放入後臺的pid
[root@oracle6 /]# echo $!
7639

6.$[1-9..]表示輸出第幾個引數
$# 表示引數的個數
$@,@* 表示所有的引數
[root@oracle6 /]# set 1 2 3 4 5 6 7 8 9 10 11
[root@oracle6 /]# echo $2
2
[root@oracle6 /]# echo $9
9
[root@oracle6 /]# echo $11
11
[root@oracle6 /]# echo $#
11
[root@oracle6 /]# echo $*
1 2 3 4 5 6 7 8 9 10 11
[root@oracle6 /]# echo $@
1 2 3 4 5 6 7 8 9 10 11

$* , $@ 區別如下
[root@oracle6 /]# set '1 2' 3 4 5 6
[root@oracle6 /]# for i in $*
> do
> echo $i
> done
1
2
3
4
5
6
[root@oracle6 /]# for i in $@
> do
> echo $i
> done
1
2
3
4
5
6
[root@oracle6 /]# 
[root@oracle6 /]# for i in "$*"
> do
> echo $i
> done
1 2 3 4 5 6
[root@oracle6 /]# 
[root@oracle6 /]# for i in "$@"
> do
> echo $i
> done
1 2
3
4
5
6